A 29-year-old woman at 7 weeks of gestation presents with lower abdominal pain and light vaginal bleeding. Her last menstrual period was 7 weeks ago. Transvaginal ultrasound shows no intrauterine pregnancy and a small adnexal mass. Beta-hCG level is 3,000 mIU per mL. She is hemodynamically stable. What is the most appropriate management?